An unidentified spokesman for Pyongyang's foreign ministry said the North will exercise its right for "pre-emptive nuclear strikes on the headquarters of the aggressors" because Washington is pushing to start a nuclear war against it.Although North Korea boasts of nuclear bombs and pre-emptive strikes, it is not thought to have mastered the ability to produce a warhead small enough to put on a missile capable of reaching the US. It is believed to have enough nuclear fuel, however, for a handful of cruder devices.Such inflammatory rhetoric is common from North Korea, but it has been coming regularly in recent days. The Pyongyang regime is angry over the possible sanctions and over upcoming US-South Korean military drills.The UN security council is set to impose a fourth round of sanctions against North Korea in a fresh attempt to rein in its nuclear and ballistic missile programmes.Russia's UN ambassador, Vitaly Churkin, the current security council president, said the council will vote on the draft sanctions resolution on Thursday morning.The resolution was drafted by the US and China, North Korea's closest ally. The council's agreement to put the resolution to a vote just 48 hours later signalled that it would almost certainly have the support of all 15 council members.The statement by North Korea's foreign ministry spokesman was carried by the country's official Korean Central News Agency.It accused the US of leading efforts to slap sanctions on North Korea. The statement said the new sanctions would only advance the timing for North Korea to fulfil previous vows of taking "powerful second and third countermeasures" against its enemies. Those measures haven't been specifically elaborated on."We gravely warn that at a time when we cannot avoid a second Korean war, the UN security council, which served as the US puppet in 1950 and made Korean people harbour eternal grudges against it, must not commit the same crime again," it said.North Korea in the statement demanded the security council immediately dismantle the American-led UN command that is based in Seoul and move to end the state of war that exists on the Korean peninsula, which continues six decades after fighting stopped because an armistice, not a peace treaty, ended the war.